Electronic transaction systems, such as credit card terminals with a card reader physically connected to a point of sale (POS) system, are known. The increasing availability of mobile terminals, such as mobile phones, have made it desirable to utilise mobile terminals for performing transactions like the payment for goods. U.S. Pat. No. 6,175,922 describes a method of approving a transaction request between a POS system and a portable electronic customer device, where the customer device receives a request for approving a transaction via a wireless communications link and, in response to an input from a user, approval data is returned from the electronic customer device to the POS system.
However, the above prior art method involves the problem that it requires a long time for checking out a given customer. When the customer reaches the check-out counter and it is his turn to pay, the cashier needs to enter a unique ID of the portable customer device, such as a phone number, into the POS system in order to enable the POS to establish the wireless communications link with the customer device. Alternatively, the customer needs to enter a unique transaction ID or POS ID into the portable customer device for the customer device to be able to contact the POS. Hence, this procedure involves the disadvantage that the time necessary from when the customer reaches the check-out counter until the actual transaction may be performed is rather long, thereby reducing the throughput of the POS. Furthermore, if a unique POS ID, such as a phone number, is used for an identification of the POS, there is a risk that another customer attempts to communicate with the same POS at the same time, resulting in a race condition. This may cause the transaction request to be sent to a wrong customer device, causing erroneous transactions and/or the need to repeat a transaction, resulting in increased transaction times and reducing the reliability of the method.